The present invention relates to preparation of 2,5-dihydrofuran from butadiene monoxide. The dihydrofuran can be hydrogenated to tetrahydrofuran, which is a good solvent for high-molecular-weight polyvinyl chloride, polyvinylidene chloride, and other difficultly soluble organic materials.
Closely related compounds can be prepared from 2,5-dihydrofuran. 2,3-dihydrofuran can be obtained by isomerizing 2,5-dihydrofuran (see, for example, U.S. Pat. No. 2,556,325); and tetrahydrofuran is readily produced from a dihydrofuran by hydrogenation.
Prior methods for preparation of tetrahydrofuran include catalytic hydrogenation of furan, which, in turn, can be prepared by decarbonylation of furfural (see, for example, U.S. Pat. No. 2,374,149 and 2,846,449). Furfural in the past has been produced from naturally occurring vegetable materials such as corn cobs and oat hulls.
In addition to obtaining tetrahydrofuran from furfural as a source material, tetrahydrofuran can also be produced by heating 1,4-butylene glycol -- for example, in an overall process using acetylene as the starting material and having the following steps: ##STR1##
Relating to the production of tetrahydrofuran from 1,4-butylene glycol by heating under specified conditions, see the disclosures of, for example, Reppe et al. U.S. Pat. Nos. 2,251,292, 2,251,835, and 2,251,895; and also Rogers U.S. Pat. No. 3,467,679.
Production of tetrahydrofuran by hydrogenation of maleic anhydride is described by T. Yoshimura in "Chemical Engineering", 1969, at page 70.
Oxidation of 1,3-butadiene to furan using a catalyst such as manganese molybdate is disclosed in U.S. Pat. No. 2,900,396. Oxidation of various organic compounds to furan using a bismuth-molybdenum catalyst at a temperature of at least 350.degree. C is disclosed in U.S. Pat. No. 3,600,405. Crotonaldehyde (propylene aldehyde) is a preferred feedstock in the process of U.S. Pat. No. 3,600,405; other feedstocks disclosed are acetals and hemi-acetals of crotonaldehyde, aldol, butadiene monoxide, crotyl alcohol, n-butyl alcohol, 1,4-butanediol and n-butyraldehyde.
The present invention is particularly concerned with preparation of dihydrofuran from an epoxide by rearrangement. An example of an epoxide rearrangement is disclosed by Heap et al. in the "Journal of the Chemical Society", 1969, at page 160. Heap et al reported that 1,3-cyclooctadiene oxide was rearranged in the presence of perchloric acid to 9-oxabicyclo(4,2,1)non-7-ene in about 50% yield: ##STR2##